1. Field of the Invention
This invention relates to a photoelectric type measuring method and device, and more particularly to improvements in a photoelectric type measuring method and device, wherein parallel scanning ray beams are utilized to measure dimensions of a workpiece to be measured.
2. Description of the Prior Art
Heretofore, there has been adopted a photoelectric type measuring device wherein rotary scanning ray beams (laser beams) are converted by a collimator lens into parallel scanning ray beams to be passed through this collimator lens and a condensing lens, a workpiece to be measured is interposed between the collimator lens and the condensing lens, and dimensions of the workpiece to be measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beam by the workpiece to be measured.
More specifically, as shown in FIG. 1, laser beams 12 are oscillated from a laser tube 10 toward a stationary mirror 14, the laser beams 12 thus reflected are converted into scanning beams 17 by a rotary mirror 16, the scanning beams 17 are converted into parallel scanning ray beams 20 by a collimator lens 18, a workpiece 24 to be measured interposed between the collimator lens 18 and a condensing lens 22 is scanned at high speed by the parallel scanning ray beams 20, and dimensions in the scanning direction (direction Y) of the workpiece 24 to be measured are measured from the time length of a dark portion or a bright portion generated due to the obstruction of the parallel scanning ray beams by the workpiece 24 to be measured.
The bright and dark portions of the parallel scanning ray beams 20 are detected as variations in output voltage of a light receiving element 26 disposed at the focal point of the condensing lens 22. Signals from the light receiving element 26 is fed to a pre-amplifier 28, where they are amplified (Refer to v), and then, fed to a segment selector circuit 30. This segment selector circuit 30 is adapted to generate a voltage V to open a gate circuit 32 only for a time t, during which the workpiece 24 to be measured is scanned, from the time of the voltage output of the light receiving element 26 and feeds the same to the gate circuit 32. A continuous clock pulse CP is fed to this gate circuit 32 from a clock pulse oscillator circuit 34, whereby the gate circuit 32 generates clock pulses P for counting the time t corresponding to the dimensions in the scanning direction, for example, the outer diameter of the workpiece 24 to be measured and feeds the same to a counter circuit 36. Upon counting the clock pulses P, the counter circuit 36 feeds a count signal to a digital indicator 38, where the dimensions in the scanning direction, i.e., the outer diameter of the workpiece 24 to be measured is digitially indicated.
In FIG. 1, designated at reference numeral 40 is a synchronous sine wave oscillator circuit, 42 a power amplifier and 44 a synchronous motor. The synchronous motor 44 rotates the rotary mirror 16 in synchronism with the clock pulses in response to synchronous signals fed from the synchronous sine wave oscillator circuit 40 in response to the continuous clock pulses CP fed from the clock pulse oscillator circuit 34, whereby the measuring accuracy is maintained.
The above-described measuring method and device have been widely utilized because the lengths, thickness and the like of moving workpiece and workpiece heated to high temperature can be measured at high accuracies in non-contact relationship therewith.
However, the diameter of the laser beams 12 in the abovedescribed high speed scanning type laser length measuring device is about 0.8-1 mm, thus causing a measuring error of 1 mm at the maximum in that condition.
In consequence, in order to reduce the diameter of the laser beams adjacent a boundary of the workpiece 24 to be measured, there has heretofore been adopted a means of measuring by use of a lens having its focal point at the boundary portion. Even in this case, it is difficult to reduce the diameter of the laser beams 12 to less than 0.08 mm, thus causing a measuring error of 0.08 mm at the maximum due to the diameter of the laser beams.
In contrast thereto, if the boundary of the workpiece to be mueasured in detected by a cross point between an output signal from a light receiving element 26 and a reference voltage, then the measuring error may be reduced to about 1 .mu.m at the maximum. In this case, however, there is presented such a disadvantage that the aforesaid measuring errors fluctuate through a change in light quantity of the laser beams 12 due to fluctuations in voltage and the like and a change in distance from the collimator lens 18 to the workpiece 24 to be measured and the like.